tailieunhanh - Báo cáo toán học: "An exploration of the permanent-determinant method"

Tuyển tập các báo cáo nghiên cứu khoa học hay nhất của tạp chí toán học quốc tế đề tài: An exploration of the permanent-determinant method. | An exploration of the permanent-determinant method Greg Kuperberg UC Davis greg@ Abstract The permanent-determinant method and its generalization the Hafnian-Pfaffian method are methods to enumerate perfect matchings of plane graphs that were discovered by P. W. Kasteleyn. We present several new techniques and arguments related to the permanent-determinant with consequences in enu-merative combinatorics. Here are some of the results that follow from these techniques 1. If a bipartite graph on the sphere with 4n vertices is invariant under the antipodal map the number of matchings is the square of the number of matchings of the quotient graph. 2. The number of matchings of the edge graph of a graph with vertices of degree at most 3 is a power of 2. 3. The three Carlitz matrices whose determinants count a X b X c plane partitions all have the same cokernel. 4. Two symmetry classes of plane partitions can be enumerated with almost no calculation. Submitted October 16 1998 Accepted November 9 1998 Also available as 9810091 The permanent-determinant method and its generalization the Hafnian-Pfaffian method is a method to enumerate perfect matchings of plane graphs that was discovered by P. W. Kasteleyn 18 . Given a bipartite plane graph Z the method produces a matrix whose determinant is the number of perfect matchings of Z. Given a non-bipartite plane graph Z it produces a Pfaffian with the same property. The method can be used to enumerate symmetry classes of plane partitions 21 22 and domino tilings of an Aztec diamond 45 and is related to some recent factorizations of the number of matchings of plane graphs with symmetry 5 15 . It is related to 1 THE ELECTRONIC .JOURNAL OF COMBINATORICS 5 1998 R46 2 the Gessel-Viennot lattice path method 12 which has also been used to enumerate plane partitions 2 38 . The method could lead to a fully unified enumeration of all ten symmetry classes of plane partitions. It may also lead to a proof of the .

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